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LDC1614: Self Distortion due to reflected waves

Takashi Onawa
Genius 13200 points
Part Number: LDC1614

Hi Team,

My customer would like to know if resonant signal generated by LDC1614 gets distortion due to refracted signals as following (Internal link : here) 
He need to clarify this point to pass their internal device review. Then, he has following two questions for the review though, could you help me to assist him to be passed the device review?

1. Do you think such reflected waves can be generated by sensor network impedance change?

2. If yes, They would like to examine the effect of noise, so could you tell me the threshold on the internal frequency count circuit?
Also, Please tell me how to mitigate the influence of noise.

Regards,

Takashi Onawa

  • 0
    TI__Mastermind 40295 points

    Takashi-san,

    By "refracted" or "reflected" waves do you mean distortion due to external signal sources?
    What is the signal that is shown in the diagram? 

  • 0 in reply to John Miller - Sensing
    TI__Genius 13200 points

    Hi John-san,

    Thanks for your prompt response on this.

    Sorry for my typo in my previous post, "Reflection" is correct.

    LDC1614 generates resonant signal for frequency count right? My customer concerns if the generated signal is reflected by sensor network and might get distortion. They would like to clarify if the self distortion introduces any errors on frequency count result.  

    Regards,

    Takashi Onawa

  • 0 in reply to Takashi Onawa
    TI__Mastermind 40295 points

    The only concern I can think of is to make sure the resonant signal does not exceed the max signal swing given in the data sheet.

  • 0 in reply to John Miller - Sensing
    TI__Genius 13200 points

    Hi John-san,

    Thanks for your comments.

    They want to understand how LDC1614 detect the resonance frequency for their risk assessments, so could you tell me the reason why you think the "only" concern is the swing level.

    In other word, could you tell me more specific explanation on why they don't need to take in account for the signal distortion due to the reflection? I need to explain that to close their question.

    Regards,

    Takashi Onawa

  • +1 in reply to Takashi Onawa
    TI__Mastermind 40295 points

    Takashi-san,


    PCB trace lengths and other conductors are short compared to the wavelength of the resonant signal on the LC.
    So thinking about this like a transmission line with transmitted and reflected signals is not very accurate.

    It is more accurate to think about this as a lumped-element circuit where the circuit that drives the resonant LC is basically a current source that uses the LC as its load. This driver has been optimized to drive LC circuits at resonance, and because this was intended to be a high-resolution, 28 bit converter, distortion has been kept to a minimum. 

    If the customer is concerned about a signal reflected off the target, the distances between the inductive coil and the target are small compared to the signal's free-space wavelength, so the argument presented above against a transmitted & reflected signal still holds.

    I hope this helps. Please let me know if you have any more questions.

  • 0 in reply to John Miller - Sensing
    TI__Genius 13200 points

    Hi John-san,

    Sorry for my slow response on this.

    Thanks to your comments, my customer accepted to close this issue. Thanks for your kindly supports on this.

    Regards,

    Takashi Onawa